Facilitating alkaline hydrogen evolution reaction on the hetero-interfaced Ru/RuO2 through Pt single atoms doping

Exploring an active and cost-effective electrocatalyst alternative to carbon-supported platinum nanoparticles for alkaline hydrogen evolution reaction (HER) have remained elusive to date. Here, we report a catalyst based on platinum single atoms (SAs) doped into the hetero-interfaced Ru/RuO2 support (referred to as Pt-Ru/RuO2), which features a low HER overpotential, an excellent stability and a distinctly enhanced cost-based activity compared to commercial Pt/C and Ru/C in 1 M KOH. Advanced physico-chemical characterizations disclose that the sluggish water dissociation is accelerated by RuO2 while Pt SAs and the metallic Ru facilitate the subsequent H* combination. Theoretical calculations correlate with the experimental findings. Furthermore, Pt-Ru/RuO2 only requires 1.90 V to reach 1 A cm−2 and delivers a high price activity in the anion exchange membrane water electrolyzer, outperforming the benchmark Pt/C. This research offers a feasible guidance for developing the noble metal-based catalysts with high performance and low cost toward practical H2 production.

3. The author claimed that the atomic ratio of Pt is 1.36% in Pt-Ru/RuO2 and Pt is the active sites for HER instead of Ru.How could such limited Pt active sites contribute to the high current density under negative potential?If this statement is correct, increasing or decreasing the amount of Pt single atoms should also have a linear relationship with their current density.However, no relevant control experiments were seen in the article.
4. The author claimed the significant decline of activity on Pt-Ru/RuO2 after the addition of SCN-, implying the essential role of Pt single atom toward activating HER.However, this experiment cannot rule out the possibility of Ru as an active site, as Ru can also be poisoned by SCN-.Besides, we also noticed that Ru/RuO2 samples themselves exhibit high HER activity (Figure 2a).Therefore, the assumption of active sites and mechanisms in this article is not accurate.5.There are some DFT calculations in this study, however, the author only calculated H* and H2O* adsorption energy.The free energy diagram for whole HER should be provided.
6.In the operando Raman spectra, the author claimed they observe that the ʋ3 peak proportions on both Pt-Ru/RuO2 and Ru/RuO2 display a dramatically faster downward trend than that of Pt/C with the increased HER potentials.However, in Figure 3a to 3c, we could not see this trend, the ʋ3 peak is very weak in all of the samples.7.In the operando XANES results, the author only measured one negative potential (-0.2V).In fact, under such a negative overpotential, most metal oxides will be reduced, so this result cannot reflect the actual changes in active sites.The catalyst reported by the author exhibits high activity even at a very low negative potential (-0.018V), therefore the author should test in-situ XANES near this potential in stages, rather than just -0.2V.
Response: This is a valuable comment.In electrocatalysis, Tafel slope can provide insights for analyzing the elementary steps and reaction mechanisms.In fact, the canonical theoretical Tafel values (120, 40, 30 mV dec -1 ) are calculated based on ideal microkinetics and many assumptions are adopted, which do not apply as such in most of the real systems.For instance, the surface and bulk concentrations of H + are assumed to be the same in the equation of deducing the theoretical Tafel values, however, it's indeed different in the realistic electrochemical conditions due to the binding capacity of the electrocatalysts, which will cause the extra H2 current and lower the Tafel slope.In addition, the Tafel behavior of real electrocatalytic interfaces is also influenced by intermediates coverages and other factors such as solvent and electrolyte ion interaction.[Int. J. Hydrogen Energy 44, 19484-19518 (2019); Sci.Rep. 5, 13801 (2015)].Therefore, the derived Tafel slope values in practical systems are not exactly the same as the theoretical values.
In our work, it can be seen that the Tafel slope is reduced from 58 mV dec -1 on Ru/RuO2 to 18.5 mV dec -1 on Pt-Ru/RuO2 after the introduction of Pt single atoms with high hydrogen coverage and binding ability.It is reported that the largely enhanced coverage of Hads intermediates usually enhances the reaction kinetics, causing the decreased Tafel slope value and driving the catalysts to follow the Volmer-Tafel mechanism in alkaline HER [ACS Catal. 13, 4752-4759 (2023); Nat. Commun. 14, 5363 (2023)].Thus, we can conclude that Pt-Ru/RuO2 follows the Volmer-Tafel mechanism in alkaline HER.In addition, similar low Tafel slopes have also been reported such as 15 mV dec -1 in Adv.Mater. 34, 2206368 (2022); 21.7 mV dec -1 in Adv.Energy Mater. 12, 2200029 (2022); 22 mV dec -1 in Nat.Commun.13, 5497 (2022); 21.6 mV dec -1 in Adv.Mater. 35, 2207114 (2023) and 18.6 mV dec -1 in Energy Environ.Sci. 16, 574-583 (2023), in which the authors attributed these low values to the Volmer-Tafel mechanism of electrocatalysts in alkaline HER.
property toward electrocatalysis, almost no interfacial water peaks can be observed on the glassy carbon plate at around 3500 cm -1 under operating conditions.In sharp contrast, these signals evidently appear in the operando Raman spectra of electrocatalysts (Figure 3a).Based on above experiments, we conclude that the D and G bands are attributed to the glassy carbon plate and the Raman lasers are evidently focus on the catalyst surface to monitor the dynamic evolution of interfacial water.

Change:
We have added the Raman spectra of glassy carbon plate under ex-situ condition and various applied potentials in Supplementary Figure 32.Corresponding descriptions have also been included from Line 331 to Line 337 in the revised manuscript: "The two carbon signals of D and G bands at around 1400 and 1600 cm -1 are derived from the glassy carbon plate (Supplementary Fig. 32a).In addition, in order to confirm that the Raman laser was focus on the surface of electrocatalyst, the operando Raman tests under various potentials in 1 M KOH solution were conducted on the glassy carbon plate without electrocatalyst.It can be clearly seen that almost no interfacial water signals (3500 cm -1 ) can be found in Supplementary Fig. 32b, which is due to the inert property of the glassy carbon plate towards the catalytic reaction."Corresponding test details are supplemented in the Methods section.4. According to the DFT results, the H2O adsorption energy of Ru* is higher than that of Pt*, indicating that Pt sites dispersed on metallic Ru are favorable for the water dissociation instead of surrounding Ru sites.Therefore, only RuO2 play the role of water dissociation.The hypothesis that H2O is more possible to be absorbed and cleaved by the Ru/RuO2 supports is actually wrong.

Response:
We fully agree with the reviewer.As shown in Figure 4c, compared with RuO2, both Pt and Ru show smaller H2O* adsorption energy, thus only RuO2 in Pt-Ru/RuO2 should be considered as the active sites for efficiently adsorbing and dissociating the H2O molecule.We are sorry to ignore the function of metallic Ru and suppose that the overall Ru/RuO2 support is responsible for water dissociation.According to Tafel slope analysis, the HER mechanism is changed from Volmer step on RuO2 (120.5 mV dec -1 ) to Volmer-Heyrovsky step on Ru/RuO2 (55.0 mV dec -1 ), suggesting the metallic Ru is also responsible for accelerating the H* combination step.This is verified by experiment results (Hupd and operando EIS tests), which disclose that in addition to Pt single atoms, the metallic Ru also contributes to the H* adsorption to promote the HER activity.H* adsorption free energy calculations in Figure 4d further indicates that Ru has a more optimized H* binding energy than RuO2.Based on above investigations, we should draw the conclusion that all Pt single atoms, Ru and RuO2 participate in the electrochemical reaction.Specifically, the water dissociation step is facilitated by RuO2 in Pt-Ru/RuO2, while both Pt single atoms and Ru boost the subsequent H* combination step, collectively contributing to enhanced alkaline HER performances.

Change:
We have corrected the related discussions in the revised manuscript.

Reviewer #2 (Remarks to the Author):
In this manuscript, the authors demonstrate that the platinum single atoms (SAs) doped Ru/RuO2 support (Pt-Ru/RuO2) catalyst exhibits a high HER activity and an excellent stability.Despite many physical/chemical characterizations and theoretical calculations were made in this work, we are afraid that several inconsistencies in mechanism and lack of novelty prevent us from a favorable recommendation of this study for publication.

Response:
We thank the reviewer for carefully reading our manuscript and we appreciate these valuable comments, which help us improve the quality of the manuscript to a large extent.Some specific comments are listed as follows: 1. Enhancing the activity and stability of PGM and its oxides for alkaline HER by incorporation of single metal atoms is a common strategy.According to my knowledge, platinum single atoms (SAs) doped Ru/RuO2 support have been investigated in many electrochemical reactions including methanol oxidation, oxygen reduction and hydrogen oxidation reactions.(Nature Communications volume 12, Article number: 5235 (2021); Croat.Chem.Acta 2017, 90 (2), 225-230).Therefore, the novelty of this manuscript is not high enough.
Response: We thank the reviewer for raising this concern about novelty for our presented work.And we thank the reviewer for pointing out these new references, which we will include in our study.Upon reviewing these works, we notice that our present work does provide significant novel insights and discussion with respect to the HER catalytic process, which is studied on Pt single metal atoms.In particular, the level of characterization and understanding of the mechanism of this catalyst under operating in-situ conditions is novel and has not been reported before.
We here want to highlight the novelties our study provides for the hydrogen evolution reaction process: Due to the optimized H* binding ability, Pt is considered as the most suitable catalyst toward the HER.However, in the alkaline medium, the catalytic activity of Pt is largely limited because of its poor water dissociation ability.In addition, RuO2, as one of the cheapest noble metal derivatives, can effectively break the water molecule but shows insufficient hydrogen recombination ability [Nat. Commun. 13, 6486 (2022)].Based on this, we experimental demonstrated that the alkaline HER activity and stability can be greatly enhanced after forming the composite (Pt-Ru/RuO2) by integrating Pt and Ru/RuO2.In the synthesis process, Pt was designed as the single atoms to largely reduce the cost and maximum the atomic utilization, meanwhile a little fraction of metallic Ru was simultaneously generated to regulate the electronic structures of RuO2 and contribute to the HER.In fact, after carefully reviewing the literatures, our synthesized Pt-Ru/RuO2 with single-atom doping and heterointerfaced structure for alkaline HER has not yet been reported so far.The catalysts in literatures listed by the reviewer are Pt single atoms doped RuO2, and their applications are MOR and ORR, respectively [Nat. Commun. 12, 5235 (2021); Croat.Chem. Acta. 90, 225-230 (2017)].
In addition, our synthesized Pt-Ru/RuO2 only delivers a low overpotential of 18 mV at 10 mA cm - 2 , which outperforms many recently reported Pt-based catalysts in alkaline HER [Nat. Commun. 14, 1711(2023) 2023)].In our work, Pt-Ru/RuO2 requires lower voltages to reach 1 A cm -2 and exhibits a higher price activity than the benchmark Pt/C, its high activity and economic efficiency in the realistic conditions further indicate a great potential toward the practical H2 production.
The present study also provides a new and previously unavailable characterization and understanding of the dynamic evolutions of the Pt single-atom catalysts during HER.Molecularlevel insights into interfacial catalytic processes and dynamic changes of electrocatalysts offer guidelines for improved design of electrocatalysts.The novelties this study provides in terms of characterization of the material and reaction processes are as follows: Operando Raman Spectroscopy is a highly sensitive technique to detect the existence states of adsorbed species during the reaction, which was employed in our work to evaluate the capacity of catalyst for promoting the water dissociation step.In addition, the element-sensitive XAS experiment under operando electrochemical conditions is the most powerful tool to monitor the real-time changes of electronic structures on catalysts for deciphering the mechanism, which was further conducted in our presented work to detect the dynamic evolutions of valence states on Pt and Ru elements under the operating potential and verify the active sites toward alkaline HER.Advanced operando XAS characterization has been absent in most prior work on Pt single-atom catalysts, for instance in the two works listed by reviewer.
2. Chronopotentiometric measurements of Pt-Ru/RuO2 and Pt/C at current densities of 10 mA cm - 2 and 250 mA cm -2 were measured on carbon paper.How about the stability of catalysts is without carbon paper?
Response: We thank the reviewer for this insightful advice.As suggested, chronopotentiometric (CP) tests of Pt-Ru/RuO2 and Pt/C with the same loading amount (0.128 mg cm -2 ) are also tested on glassy carbon (GC) electrode (surface area: 0.196 cm 2 ) and nickel foam (NF) (surface area: 1 cm 2 ) for sake comparison.
Due to the flat and small surface area of the GC electrode, the generated H2 bubbles are difficult to be released from the catalyst surface, hindering the electrochemical interaction with electrolyte [Angew.Chem.Int.Ed. 61, e202103824 (2022); Carbon 186, 282-302 (2022)].Thus we conducted the CP tests at the current density of 10 mA cm -2 for 42 hours on the GC electrode with a rotating rate of 1600 rpm (to remove the generated bubble).As shown in Figure R1, the CP test of Pt-Ru/RuO2 is stably operated for 42 h with only 4 mV overpotential increase at 10 mA cm -2 , whereas Pt/C shows a large activity loss (85 mV) after operating for 42 h.In addition, compared with the dramatic increase of the overpotential on NF-supported Pt/C, a much smaller increase of overpotential is found on the NF-supported Pt-Ru/RuO2 at the large current density of 250 mA cm -2 for 150 h.Above measurements indicate that the Pt-Ru/RuO2 still possesses an excellent HER stability in the alkaline electrolyte on both glassy carbon electrode and nickel foam, outperforming the commercial Pt/C.3. The author claimed that the atomic ratio of Pt is 1.36% in Pt-Ru/RuO2 and Pt is the active sites for HER instead of Ru.How could such limited Pt active sites contribute to the high current density under negative potential?If this statement is correct, increasing or decreasing the amount of Pt single atoms should also have a linear relationship with their current density.However, no relevant control experiments were seen in the article.

Response:
We thank the reviewer for raising this point.As suggested by the reviewer, in addition to our reported Pt-Ru/RuO2, we have also prepared two other catalysts by halving and doubling the inputs of Pt precursor and their atomic ratios of Pt are determined to be 0.92% and 3.06% by ICP, respectively.Corresponding LSV results show that after only doping 0.92% Pt, the HER activity of Pt-Ru/RuO2 is obviously improved compared with the Ru/RuO2 owing to the introduction of highly active Pt sites.However, with further increasing the doped Pt amount from 1.36% to 3.06%, its activity decreases, which may be attributed to the formation of aggregated Pt clusters [J.Am.Chem. Soc. 145, 17577-17587 (2023); Nat. Commun. 13, 6875 (2022)].In fact, the relationship between the doped amount of single atoms and the catalytic performances in electrocatalysis is more likely to be volcanic rather than liner.This is because that the activity is closely related to the number of active sites involved in the electrochemical reaction, which does not indefinitely increase with the increased amount of doped single atoms.When the amount of input precursor is increased to a certain level, clusters or nanoparticles are formed, which inevitably limits the sufficient atom utilization as well as fails to induce the efficient interactions, causing the decreased catalytic performance [Angew.Chem. Int. Ed. 61, e202209486 (2022)].Therefore, the optimal Pt doped amount in Pt-Ru/RuO2 is 1.36%, contributing to the best HER activity in 1 M KOH solution.
Actually, after doping only 1.36 at% Pt, the Pt-Ru/RuO2 shows a significant activity increase compared with the Ru/RuO2 (93 mV of overpotential decrease at 10 mA cm -2 ).Such an enhancement is achieved by doping Pt with optimized H* binding energy to activate HER, which is confirmed by both experiment and DFT calculations.Although the doping amount is only 1.36%, Pt species in our work are designed as the single atoms to ensure the maximum atomic utilization and efficient interaction in catalytic reaction, which are the advantages of the single-atom materials compared with conventional nanoparticle catalysts.Indeed, the phenomena of an obvious activity enhancement after single-atom doping are commonly reported in many literatures.5.There are some DFT calculations in this study, however, the author only calculated H* and H2O* adsorption energy.The free energy diagram for whole HER should be provided.

Response:
We thank the reviewer for providing this valuable suggestion.As suggested, we have added the free energy calculations for whole HER process (H2O* dissociation and H* adsorption) in the revised manuscript.As demonstrated in the H2O* dissociation free energy diagram in Supplementary Figure 39, Pt single atoms possess the largest energy barrier to break the molecule bond in H2O.In addition, although Ru sites in metallic Ru and RuO2 show similar energy barriers, considering that H2O is prone to be adsorbed on RuO2 (H2O adsorption energy in Figure 4c), the water dissociation step is more possible and easily to be achieved by the RuO2 in Pt-Ru/RuO2.Corresponding H* adsorption free energy diagram in Figure 4d reveals that Pt sites deliver the most optimal value of 0.115 eV among all studied active sites, indicating that Pt single atoms are in favor of boosting the H* combination step.It is also noted that the H* free energy on Ru is closer to zero than RuO2, suggesting that Ru also contributes to the H* adsorption and H2 generation.These DFT calculation results are in agreement with the experimental results.
Change: Following the suggestion of the reviewer, we have calculated the free energy for whole HER process (H2O* dissociation and H* adsorption) and added them in the Supplementary Figure 39 and Figure 4d, respectively.Related discussion has also been clarified from Line 406 to Line 416 in the revised manuscript: "The H2O* dissociation free energy in Supplementary Fig. 39 further indicates that Pt single atoms is difficultly break the H2O molecule due to the largest energy barrier.In addition, although Ru and RuO2 have the similar energy barriers, considering the stronger ability of adsorbing H2O on RuO2, the water dissociation is more efficient and easier to be completed by RuO2 rather than Ru.On the other hand, the H* adsorption free energy on all sites in Pt-Ru/RuO2 were also calculated to examine their abilities for activating the followed H* combination step.As shown in Fig. 4d, compared to the other active sites, Pt sites deliver the optimal value of 0.115 eV, demonstrating that the incorporated Pt single atoms are favorable for boosting the H* combination step. 61-63It is also noted that the H* adsorption free energy on Ru is closer to zero than RuO2, which suggests that Ru also contributes to the H* adsorption and H2 generation.".In addition, corresponding calculation methods for free energy have also been added in the Methods section.6.In the operando Raman spectra, the author claimed they observe that the ʋ3 peak proportions on both Pt-Ru/RuO2 and Ru/RuO2 display a dramatically faster downward trend than that of Pt/C with the increased HER potentials.However, in Figure 3a to 3c, we could not see this trend, the ʋ3 peak is very weak in all of the samples.
Response: We thank the reviewer for raising this point.Indeed, as we mentioned in the manuscript, the broad Raman peak of interfacial water at around 3500 cm -1 is constituted by three kinds of coordinated water molecules on the catalyst surface (ʋ1 at 3225 cm -1 , ʋ2 at 3450 cm -1 and ʋ3 at 3615 cm -1 ), in which the ʋ3 peak assigned to inactive dangling O-H bond only takes up a small portion.Generally, the higher the water dissociation ability of a catalyst, the smaller fraction the ʋ3 peak.And the ʋ3 peak proportion decreases further with the increase of the applied catalytic potentials, thus it is hard to directly distinguish the dynamic evolution trend of the ʋ3 peak by visual inspection during the HER.
As shown in Supplementary Figure 33-35 and Supplementary Table 7, after carefully analyzing and fitting these broad peaks, the ʋ3 peak proportions for all samples are elaborately evaluated, corresponding values are close to the reported values in the reported literatures [Adv. Energy Mater. 13, 2203136 (2023);Adv. Funct. Mater. 33, 2212321 (2023);Adv. Funct. Mater. 32, 2109556 (2022)].Meanwhile, it can be seen that the ʋ3 peak fractions decrease with negatively increasing the applied potentials, in which Pt/C shows a relative slower downward trend compared with the Pt-Ru/RuO2 and Ru/RuO2, indicating its unsatisfied water dissociation ability for alkaline HER.
7. In the operando XANES results, the author only measured one negative potential (-0.2 V).In fact, under such a negative overpotential, most metal oxides will be reduced, so this result cannot reflect the actual changes in active sites.The catalyst reported by the author exhibits high activity even at a very low negative potential (-0.018 V), therefore the author should test in-situ XANES near this potential in stages, rather than just -0.2 V.
In order to experimentally confirm this, we have further conducted the operando Raman characterizations of Ru and RuO2 under HER operating conditions (Supplementary Figure S36 -38).After carefully fitting the interfacial water peak in these spectra, we report in Supplementary Figure S39 that the ʋ3 peak proportion at 3615 cm -1 on RuO2 alone displays a clearly faster downward trend in HER process than that on Ru alone, indicating its greater capability for cleaving the water bond.More importantly, pure RuO2 exhibits a similar downward trend as the heterointerfaced Ru/RuO2 during more cathodic HER electrode potentials: this is a testament and validation to our hypothesis that the key water activation and dissociation sites on Ru/RuO2 are located on the surface of RuO2 rather than on the Ru phase, and this is consistent with our theoretical calculations.Moreover, it is calculated that the decline rate of ʋ3 peak proportion on RuO2 (52.4%) is slightly slower than that on Ru/RuO2 (57.5%), which can be attributed to the electronic interaction between Ru and RuO2 in Ru/RuO2.As discovered in Supplementary Figure S42, Bader charge analysis reveals that electrons transfer from Ru to RuO2 in Ru/RuO2, which can modulate the electronic structure of RuO2 to facilitate the catalytic ability [Adv. Mater. 35, 2208821 (2023); Nat. Commun. 13, 5448 (2022); Angew.Chem. Int. Ed. 61, e202202519 (2022)].

Change:
We have added the operando Raman spectra of Ru and RuO2 under HER operating conditions and corresponding fitting results of the interfacial water peaks in Supplementary Figure S36-38.The ʋ3 peaks proportions at nearly 3615 cm -1 during HER on RuO2, Ru and Ru/RuO2 are also supplemented in Figure S39 and Supplementary Table 7. Related clarification has also been added from Line 349 to Line 361 in the revised manuscript: "As shown in Supplementary Fig. 36-38, the operando Raman tests were further conducted on Ru and RuO2.After carefully fitting these spectra, it can be obviously observed that RuO2 exhibits a faster downward trend of ʋ3 peak proportion than that on Ru in HER process, confirming its greater capability for cleaving the water bond.Significantly, RuO2 exhibits a similar downward trend as the Ru/RuO2 during more cathodic HER potentials, which validates that RuO2 is the main active site for water activation and dissociation step in Ru/RuO2 instead of Ru.Furthermore, it is calculated that the decline rate of ʋ3 peak proportion on RuO2 (52.4%) is slightly slower than that on Ru/RuO2 (57.5%), which may be attributed to the electronic interaction between Ru and RuO2 in Ru/RuO2 (Supplementary Fig. 39).Based on above investigations, it can be experimentally concluded that RuO2 is primarily responsible for the water dissociation step while both Pt single atoms and Ru facilitate the followed hydrogen combination step, collectively leading to the remarkable alkaline HER activity of Pt-Ru/RuO2, and this is further validated by DFT calculations.".
2. The operando XAFS characterization in this study is not rigorous enough.They measured three edges for each element including pristine state and OCP, which means there is only one data under reaction condition.This is not accurate enough for getting any conclusion from operando experiments (Chem. Rev. 2021, 121, 2, 882-961).That's why we suggest the authors should test in-situ XANES near -0.018V in stages in our last review report, which means a series of data under reaction condition should be collected for comparison.However, the authors still just measure one data at -0.018V.

Response:
We thank the reviewer for this important suggestion.While we, in principle, fully agree with the collection of ever more spectroscopic data for an ever better characterization of the catalysts under all possible conditions, we have to be also realistic and emphasize that the operando XANES tests are extremely time-consuming measurements conducted at synchrotron facilities not in a lab environment.This is why the expected delay time of 9-12 months from applying for additional own beamtime to performing the synchrotron experiments appears out of proportion.
However, following and in order to satisfy the reviewer's suggestion, we have "borrowed" some extra beamtime from colleagues to perform the suggested measurements.We now present additional spectroscopic data measured at the Pt L3-edge and Ru K-edge of our sample at the pristine state, OCP, and HER operating potential of -0.018 V and -0.04 V, and the operando XANES measured at -0.04 V is added in Supplementary Figure 40.
The new data evidence that the white line of the Pt L3-edge displays a clearly lower energy shift when the applied potential was changed from OCP to -0.018 V (at which the current density is 10 mA cm -2 ), indicating that the chemical oxidation state of Pt single atoms reduced during cathodic HER.In addition, the valence states of Pt further decreased with the negative increase of potential to -0.040 V. Similarly, the energy position of the Ru K-edge XANES in Supplementary Figure 40b shows lower energy shifts from OCP to -0.018 V and further to -0.04 V, suggesting a continuous decrease in oxidation states of Ru element.Therefore, according to the potentialdependent operando XANES results tested at pristine state, OCP and two HER operating potentials (-0.018V and -0.04 V), it is convincing now to get a solid conclusion that both Pt and Ru elements in the Pt-Ru/RuO2 are active sites and efficiently activate the alkaline HER [Nat. Commun. 13, 1143(2022); J. Am.Chem. Soc. 143, 17117-17127 (2021); Nat. Catal. 2, 134-141 (2019)].

Change:
We have added the operando XANES spectra of Pt L3-edge and Ru K-edge at the pristine, OCP and HER operating potentials of -0.018 V and -0.040 V in the Supplementary Figure 40.Related clarification has also been added from Line 373 to Line 380 in the revised manuscript: "In order to further confirm that both Pt and Ru are active sites during HER, the lower HER operating potentials of -0.018 V (at which the current density is 10 mA cm -2 ) and -0.040 V were applied on Pt-Ru/RuO2 to conduct the operando Pt L3-edge and Ru K-edge XANES.Similarly, both white line peak position of Pt and adsorption edge of Ru continuously shift to lower energy with the negatively increased potentials, indicating their decreased valence states in the HER process (Supplementary Figure 40).Thus, the potential-dependent operando XANES results further verify that both Pt and Ru elements in Pt-Ru/RuO2 are active sites toward the alkaline HER.".

Supplementary
Figure 32.(a) The ex-situ Raman spectrum of the glassy carbon plate without catalyst and electrolyte.(b) The operando Raman spectrum of the glassy carbon plate in the electrolytes under various applied potentials.

Figure R1 .
Figure R1.The stability tests of Pt-Ru/RuO2 and Pt/C (a) on glassy carbon electrode at 10 mA cm -2 for 42 h and (b) on nickel foam at 250 mA cm -2 for 150 h, respectively.

Figure 4d .
Figure 4d.The H* adsorption free energy values for Pt, Ru and RuO2 sites in Pt-Ru/RuO2.
; J. Am.Chem.Soc.145,21432(2023);EnergyEnviron.Sci.16,4093-4104(2023)].Furthermore, the price activity of Pt-Ru/RuO2 reaches almost 15 times higher than commercial Pt/C and Ru/C, which exhibits a good comprise with respect to the HER performance and cost.More importantly, compared with the half-cell electrochemical test, the anion exchange membrane water electrolyzer (AEMWE) test under a much larger operating current density is more crucial and meaningful, which can provide a more accurate evaluation of the catalyst efficiency in the practical application[Energychem 4, 100087 (2022); Carbon Neutralization.1,26-48(2022)].However, until now in most of literatures reporting on alkaline HER catalysts, corresponding AEMWE performances have not been investigated[Adv.Mater.35,2301133 (2023); Angew.